The present invention relates to a process for blast cleaning articles--particularly those with internal passageways, which have a tendency to trap the blast media.
A variety of processes have been developed to blast clean articles with internal passageways and minute outlet holes. Such articles include, for example, jet turbine blades, where blast cleaning is periodically performed to remove oxides and other deposits. The blasting process includes directing a stream of air carrying a blast media through the article. The media is a particulate matter, so that the process is akin to "sand blasting."
Typically, the blast media is aluminum oxide or silicon carbide. Both aluminum oxide and silicon carbide have a tendency to embed in the surface of the article during blasting. The embedded aluminum oxide is relatively inert and hinders welding and brazing of the article. The embedded silicon carbide lowers the melting point of the article and may cause premature melting.
The blasting process further suffers in that the blast media tends to become lodged within the outlet holes and to accumulate inside the internal passageways of the article. The outlet holes must be manually cleared with a protrusion that is sufficiently narrow to fit within the outlet holes. This technique suffers in that it is tedious and requires excessive labor. Further, the blast media that has accumulated within the internal passageways cannot be properly removed in this manner.
Alternatively, the article can be cleaned in an autoclave, wherein the article is soaked in a hot caustic alkaline bath. This technique suffers in that additional equipment is necessary to autoclave the article and to handle the dangerous solutions. Further, the surface of the article or any article coatings are also leached in the autoclave.